I am in the process of connecting several qt110 sensors to my arduino. but i have some problems with the sensitivity of them.

basic setup: basically one pin of the arduino serves as the Vcc for all the sensors. power requirements for these sensors is really low. all the outputs of the sensor (4)are going to the other pins on the arduino to collect the data. but that has not yet been build.

I'm still in the process of figuring out how those sensors work. I've made a pcb with a sensor and a optocoupler as a output buffer. there is a 10nF capacitor and a 470k resistor parallel to the sensor pins so to set the sensitivity. gain is high (not connected) and both the option pins are on Vcc.

the setup is going to be used behind a glass plate of 8mm thick with some white foil behind it with written marks on it. the whole plate is then backlited with some 12volt bulbs as soon as you touch the glass (or get with your hands in reach of a sensor...) the pcb with the sensor and a led are a mere 5 cm behind the glass, but the electrode (a naked wire of 10cm) is touching the glass.

At the moment with my test setup i have to press really hard at the plate and even that not allways works. i've experimented with grounding myself and the - of the power supply, but that does'nt help.

is there someone who has worked whith this kind of things before? what am i doing wrong?

Well as it turned out, the size of the sensing wire was to small. it shoud be at least two dimensional, not one. I have made a grid of copper wire size 5x5 cm and now i can sense through glass and wood at the same time in thickness of about 1 cm. and the grid is not evben touching the glass or wood!